This paper reports recent progress in the field of
γ-ray diagnosis of fast ions in the JET tokamak. The γ-rays, born in
nuclear reactions between fast ions and main plasma impurities and/or plasma
fuel ions, are analysed with a new modelling tool (the GAMMOD code) that has
been developed for a quantitative analysis of the measured γ-ray energy
spectra. The analysis of the γ-ray energy spectra identifies the
different fast ions giving rise to the γ-ray emission and assesses the
effective tail temperatures and relative concentrations of these fast ions.
This assessment is possible, since the excitation functions for the
different nuclear reactions are well established and exhibit a threshold
or/and a resonant nature. The capabilities of the γ-ray spectral
analysis are illustrated with the examples from the recent γ-ray
diagnostic measurements of 4He, 3He, deuterium and hydrogen ions
accelerated by ion-cyclotron resonance frequency heating in JET.
Simultaneous measurements of several fast ion species, including highly
energetic α-particles, are demonstrated. In addition to the
γ-spectroscopy, tomographic reconstructions of the radial profile of the
γ-ray emission are performed using the JET neutron profile monitor, thus
providing direct measurements of the radial profiles of fast ions in JET.
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